The invention relates to a process for the preparation of polymers of carbon monoxide with one or more olefinically unsaturated compounds.
Linear polymers of carbon monoxide with one or more olefinically unsaturated compounds, in which the polymer units originating from carbon monoxide on the one hand and the polymer units originating from the olefinically unsaturated compounds on the other hand, occur in a substantially alternating arrangement, and can be prepared by contacting the monomers at an elevated temperature and pressure and in the presence of a diluent in which the polymers are insoluble or virtually insoluble with a solution of a catalyst composition that suits the purpose.
As a rule, the polymerization is carried out by introducing a catalyst solution into a reactor which contains the monomers and the diluent and which is at the desired temperature and pressure. During the polymerization the polymers are obtained in the form of a suspension in the diluent. When the required degree of polymerization has been achieved, the polymerization is terminated, as a rule by cooling the reaction mixture to room temperature and releasing the pressure. The polymer is then removed from the suspension, washed and dried.
In regards to the diluent to be used in the polymerization, lower aliphatic alcohols such as methanol are preferred, since it has been found that the catalyst compositions suiting the purpose of the present invention have the highest polymerization rate when dissolved in methanol. A drawback of the use of lower aliphatic alcohols as a diluent for the aforesaid polymerization is that the prepared polymers contain 4000-15,000 ppmw of the applied alcohol, and that this quantity of alcohol cannot be removed from the polymer even by prolonged and careful drying. It must be assumed that this quantity of alcohol is chemically bonded to the polymers, since it has been found that the alcohol content is hardly changed after extrusion of the polymers at temperatures of around 270.degree. C.
The high alcohol content can be a problem if the present polymers are used as packaging material for foodstuffs. It is therefore worth devoting attention to the reduction of this high alcohol content.
Extensive research has been carried out on this subject. Initially, the desired goal was to treat the polymers at high temperature with water or steam. Although the alcohol content of the polymers could be reduced in this way, the resulting deterioration in the properties of the polymers was such that these methods had to be rejected.
In the course of continued research into this subject, it has now surprisingly been found that in the preparation of the aforesaid alternating polymers using one or more lower aliphatic alcohols as diluent, polymers with a reduced alcohol content can be prepared by adding water to the diluent.